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Intermittent loss of fuel injection

chimaera4chimaera4 Member Posts: 2
edited April 2014 in Pontiac
98SE 170K wouldn't start after sitting overnight. Replaced the fuel pump because it was getting noisy and I thought that was the problem. It ran for several days great and then died on the freeway. It will crank but further testing showed no pulse to injectors. Before the mechanic could get any further diagnosis it started working again and we can't get it to act up. Any ideas?
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    imidazol97imidazol97 Member Posts: 27,154
    I know it's a dumb question now, but you need to know if it's getting spark to the plugs. If both are missing, it makes the crankshaft position sensor suspect or a computer (PCM).

    2014 Malibu 2LT, 2015 Cruze 2LT,

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    chimaera4chimaera4 Member Posts: 2
    Thanks for the reply

    I was unable to get kick with starter fluid when I first thought it was the fuel pump. Also I have had some very subtle rpm pulsing (maybe 200rpm) at 55-70mph for several months now, but that also was intermitant and I have not seen a check engine light. If I can actually get it to die again I will check spark. I find it odd that it is all or nothing. Ground maybe?
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    imidazol97imidazol97 Member Posts: 27,154
    You might still have a fuel pump problem. You need to determine spark and injector pulses when this happens. You can use a 197 little running light bulb with the wires for contacts that you straighten and put this into a lead for one of the injectors. (Take one off in advance so you know how and it's been unsnapped in advance so it works more easily.)

    You could have a bad wire connection going to the fuel pump. YOu could have a defective fuel pump. You could have a crankshaft position sensor that is not reading so no spark and no injector pulse. You could have a bad PCM.

    The rpm pulsing locked up at 55 could be a valve in the transmission that controls the percent lockup on the torque converter clutch (it's never 100%) and that valve wears in its cylinder and becomes sticky (gunk from not changing fluid may help that happen) and it changes the lockup amount while you're driving. On most cars becomes more noticeable after the car has been driven a long time like half an hour or more. See if it does it at same engine rpms while the brake is held slightly to disengage the torque converter clutch.

    It may be a good investment to get a fuel pressure gauge with a long enough tube to reach from the fuel line connector to the windshield so you can tape it to the windshield while driving. You can see if the pressure is staying high enough.

    2014 Malibu 2LT, 2015 Cruze 2LT,

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